a. Field of the Invention
This invention relates to the control of hydrocarbon production using plunger lift systems. More specifically, it relates to controllers using measurements of conditions in subsurface wells to operate non-linear artificial intelligence processes to sequence the operation of plunger lift devices.
b. Discussion of the Prior Art
The control of oil and gas production wells are an on-going concern of the petroleum industry due, in part, to the monetary expense involved as well as the risks associated with environmental and safety issues.
In many hydrocarbon wells, that is gas and oil wells, as described in greater detail below, fluids accumulate within the well casing and production string which block the flow of the formation gas or oil into the borehole, and such accumulations reduce the production of hydrocarbons from the well. As used herein, “fluids” primarily refers to a combination of naturally occurring liquids and emulsions, including water, oil, paraffin or combinations thereof. As fluids accumulate within the well casing and production string, often referred to as “tubing string” or “tubing”, the production of hydrocarbons from the well may diminish, and may ultimately fail due to the effect of pressure buildup of such fluids on the formation. Currently, the state-of-the art technique for removing accumulated fluids from the well casing and production string is through the use of plunger lift systems.
State-of-the art plunger lift production systems include a cylindrical plunger. In such a system, the cylindrical plunger normally resides at the bottom of the borehole, and is sized to travel through the production string extending from a location adjacent to the producing formation down in the bottom of the borehole upward to the surface equipment located at the hydrocarbon receiving end of the borehole. In general, fluids in the borehole that inhibit the flow of hydrocarbons out of the formation tend to collect in the lower portion of the production string. Periodically, a valve, typically a motor valve, in the production string at the surface of the well is opened at the surface. This allows accumulated reservoir pressure within the well to drive the plunger up the production string. The small clearance between the plunger and the well production string is such that the plunger carries with it to the surface a load of accumulated blocking fluids. The accumulated fluids are then ejected out of the top of the well, thereby allowing hydrocarbons to flow more freely from the formation into the well bore and be delivered to a distribution system at the surface. After the flow of gas has once again been restricted due to the further accumulation of fluids downhole, the surface valve of the well is closed, and the plunger, due to its own weight, then falls back down the production string to the bottom of the borehole. While the valve is so closed, the pressure within the well generally increases again. If the pressure is allowed to build to a strong enough level, the pressure will be strong enough to lift the plunger and another load of fluids to the surface of the well when the valve is reopened.
In plunger lift production systems, there is a requirement for the periodic operation of a motor valve at the surface of the wellhead to control the flow of fluids from the well to assist in the production of hydrocarbons and removal of fluids from the well. These motor valves are conventionally controlled by timing mechanisms and are currently programmed in accordance with principles of reservoir engineering, which determine the length of time that a plunger lift control valve should be either “closed” and restricted from the flowing of gas or liquids to the surface, and the time the plunger lift control valve should be “opened” to more freely produce.
If the plunger lift control valve is left opened or closed for too long of a time, there will be a loss of well production and the producing formation may be damaged. Furthermore, pressure buildup within a well can cause the plunger to rise to the surface at excessive speeds, which can cause serious damage to the surface components of the well and cause hydrocarbons and fluids from the well to leak into the surrounding environment. Not only does this present a safety risk to workers at the surface of the well, but it also presents serious environmental concerns. It is therefore seen that control of the plunger lift control valve is critical to maintain proper pressure and production balance within the well by avoiding having it be open or closed for too long or too short of a time.
It is extremely impractical to manually open and close the plunger lift control valve for each well. As a consequence, automatic controllers are currently used to open and close the motor valve. Generally, the criterion used in most systems for operation of the plunger lift control valve is strictly one of the elapse of pre-selected time periods. In most systems, measured well parameters, such as pressure and temperature, can be used to override the timing cycle in special conditions.
For example, in the patent prior art, U.S. Pat. No. 4,150,721 (Norwood) discloses a battery operated gas well controller system which utilizes digital logic circuitry to operate a well in response to a timing counter and certain measured well parameters. U.S. Pat. Nos. 4,352,376 and 4,532,952 (Norwood) disclose similar controllers comprising the use of a microprocessor. U.S. Pat. No. 4,354,524 (Higgins) discloses a pneumatic timing system which uses injected gas to artificially lift liquids to a well surface. U.S. Pat. No. 4,355,365 (McCracken) discloses a system for electronically operating a well in accordance with timing techniques wherein the well is allowed to flow for a pre-selected period of time and then closed for a second pre-selected period of time to effect the production from the well. U.S. Pat. No. 4,921,048 (Crow) discloses an electronic controller which detects the arrival of a plunger and monitors the time required for the plunger to make each trip to the surface. U.S. Pat. No. 5,146,991 (Rogers, Jr.) discloses a plunger lift well which evaluates plunger lift speed. U.S. Pat. No. 5,878,817 (Stastka) discloses a controller which opens the plunger lift control valve based on the measurement of the pressure difference between the gas in the tubing line and the pressure of gas in the sales line, and in addition uses the speed of the plunger to adjust valve operation. Similarly, U.S. Pat. No. 6,595,287 (Fisher) controls valve operation based on the pressure difference between sales line pressure and well casing pressure. U.S. Pat. No. 5,984,013 (Giacomino) uses plunger arrival time to adjust the subsequent valve opening and closing times.
It is currently observed that relatively simple, timed intermittent operation of plunger lift control valves is often not adequate to control outflow so as to optimize hydrocarbon production from wells. As a consequence, sophisticated computerized controllers positioned at the surface of production wells have been used for control of devices, such as the plunger lift control valves. Additional systems have been developed that relate to: (1) surface controller systems using a surface microprocessor; and (2) downhole controller systems which are initiated by surface control signals.
Surface controller systems generally teach computerized systems for monitoring and controlling a gas/oil production well whereby the control electronics is located at the surface and communicates with sensors and electromechanical devices near the surface. An example of this system is disclosed in U.S. Pat. Nos. 4,633,954 (Dixon) and 4,685,522 (Dixon), which describe a fully programmable microprocessor controller which monitors downhole parameters, such as pressure and flow, and controls the operation of gas injection to the well, outflow of fluids from the well, or shutting in of the well to maximize output. Another example of a controller system of this type is disclosed in U.S. Pat. No. 5,132,904 (Lamp), which further describes a feature where the controller includes serial and parallel communication ports through which all communications to and from the controller pass. Hand held devices or portable computers capable of serial communication may access the controller. A telephone modem or telemetry link to central host computer may also be used to permit several controllers to be accessed remotely. It is well recognized that petroleum production wells using surface based controllers will have increased production efficiencies and lower operating costs than downhole microprocessor controllers.
In general, although controller systems have become much more complex, they still do not fully optimize well production and often require a great deal of operator inputs. What is needed is a plunger lift system that optimizes the open and close cycles of the motor valve based on minimal input. Additionally, well operation and production varies between different wells and can even change from cycle to cycle within the same well. For example, the gas pressure within a well will vary from well to well and can significantly change during the life of that well. Because each well will have its own unique properties, the automatic controller closing and opening the plunger lift control valve must be suitable for use on a wide variety of wells and be flexible enough to adjust to the changes that often occur during the life of the well to provide ongoing optimum production. Ideally, the operation of a plunger lift control valve by an automatic controller system would be able to approximate the operation of a controller system by an ever present and vigilant human operator.